1. Field of the Invention
The present invention relates to the biological control of postharvest diseases in fruit. More particularly, this invention relates to a method for biologically controlling postharvest rots on fruits using a strain of Pseudomonas cepacia, "P. cepacia." and the antifungal compound, pyrrolnitrin, produced therefrom.
2. Description of Prior Art
Postharvest diseases of fruit cause 15 to 25% losses yearly in the fruit industry worldwide. Fungicides, the major weapon in combatting these diseases, are often ineffective and pose hazards to humans and the environment. Therefore, a critical need exists for new methods to control postharvest diseases.
Recently, it has been shown that the postharvest treatment of fruit with antagonistic microorganisms is an effective approach to the control of postharvest rots. Remarkable success was shown in the control of brown rot in peaches caused by Monilinia fructicola (Wint.) Honey with Bacillus subtilis. Pusey et al. [Plant Dis. 68: 753-756 (1984)]. De Matos was able to reduce mold incidence from 35% to 8% when a species of Trichoderma was inoculated with Penicillium digitatum into lemon peel. De Matos, Ph.D Dissertation, University of California, Riverdale, (1983). Singh and Deverall demonstrated biocontrol with bacterial antagonists to the citrus pathogens Alternaria citri Pierce, Geotrichum candidum link. ex Pers., and P. digitatum. Singh et al. [Trans. Br. Mycol. Soc. 83: 487-490 (1983)]. Dipping wounded citrus fruit in suspensions of bacterial cells, particularily a strain of Bacillus subtilis (Ehrenber) Cohn, delayed decay by the three rot pathogens.
Trichoderma viride Pers. & S. F. Gray applied to strawberry plants in the field was shown to partially control gray-mold on strawberry fruits after harvest. Tronsmo et al. [Neth. J. Plant Pathol. 83(suppl. 1): 449-455 (1977)]. Also, partial control of rot in apples caused by B. cinerea flower infection was obtained by applying conidia T. harzianium Rifai to apple trees during bloom. Control was comparable to prior known fungicidal treatments. Tronsmo et al. [Plant Dis. 64:1009 (1980)].
P. cepacia has been reported to reduced southern maize leaf blight caused by Bipolaris maydis in greenhouse tests, Sleesman et al. [Phytopathology 66: 1214-1218 (1976)], decrease peanut Cercospora leaf spot and tobacco Alternaria leaf spot in the field, Spur [Phytopathology News (Abstract) 74:17 (1978)], and to control damping off of onion seedlings by Fusarium oxysporum f.sp. cepae. Kawamoto et al. [Plant Dis. Rep. 60: 189-191 (1976)].